Magnetic recording media

ABSTRACT

MAGNETIC RECORDING MEDIA COMPRISING A NON-MAGNETIC SUPPORT AND A MAGNETIC LAYER BASED ON A MAGNETIC PIGMENT DISPERSED IN A BINDER AND CONTAINING A SMALL AMOUNT OF A LIQUID MIXTURE OF BRANCHED FATTY ACIDS HAVING AT LEAST 95% BY WEIGHT OF C12 TO C18 FATTY ACIDS AND AT LEAST 40% BY WEIGHT OF BRANCHED C18 FATTY ACIDS.

United States Patent 3,704,152 MAGNETIC RECORDING MEDIA Hans JoergHartmann, Wachenheim, Georg Schnell, Ludwigshafen, Gerhard Werst,Neustadt, Horst Grosselfinger, Mannheim, Job-Werner Hartmann,Ludwigshafen, and Hansjoerg Bipp, Limburgerhof, Germany, assignors toBadische Anilin- & Soda-Fabrik Aktiengeseilschaft, Ludwigshafen (Rhine),Germany No Drawing. Filed Sept. 10, 1970, Ser. No. 71,260

Int. Cl. H01f /02 U.S. Cl. 117-235 6 Claims ABSTRACT OF THE DISCLOSUREMagnetic recording media comprising a nonmagnetic support and a magneticlayer based on a magnetic pigment dispersed in a binder and containing asmall amount of a liquid mixture of branched fatty acids having at least95% by weight of C to C fatty acids and at least 40% by weight ofbranched C fatty acids.

The present invention relates to improved magnetic recording media,particularly magnetic tapes which have improved resistance to aging andabrasion and cause less corrosion.

Magnetic tapes are often used on recording equipment for many hoursunder widely varying climatic conditions, for example at high altitudeswhile exposed to the action of strong ultraviolet radiation, underconditions of high temperature and humidity or even at temperaturesbelow freezing. Sometimes equipment with the magnetic tape thereon isstored for long periods under unfavorable climatic conditions so thatthe occurrence of corrosion phenomena on the metal parts with which thetape comes into contact would be very detrimental. These are howeververy likely to occur when binders containing chlorine are employed.

Modern magnetic recording media are also required not to exhibit anyageing of the magnetic layer when stored in the air, particularly in airenriched with ozone. Finally, the magnetic recording media shoulddeposit as little as possible parts of the equipment and at the sametime should exhibit low sliding friction.

It is known that lubricants such as wax, petroleum jelly, esters oramides of fatty acids and parafiin wax may be added to magnetic layers.As disclosed in German Printed Application No. 1,278,513, many of theprior art lubricants, such as the esters of fatty acids, readily exudeand cause undesirable tackiness of the layer. The addition of esters offatty acids such as stearyl stearate also gives unsatisfactoryelectroacoustic results. Moreover, these additives as well as addedfatty acids such as n-stearic acid or mixtures of fatty amides andparaffin Wax tend to form deposits on those parts of the equipment withwhich the tape comes into contact.

We have now found that magnetic recording media comprising anon-magnetizable base and a firmly adherent layer of particulatemagnetic pigment dispersed in a binder with or without additives areparticularly advantageous and exhibit improved resistance to abrasionand ageing and cause less corrosion when the magnetic layer contains asan additive from 2 to 10% by weight, based on the dry weight of themagnetic layer, of a mixture of predominantly branched, fatty acidscontaining at least 95% by weight of fatty acids having twelve toeighteen carbon atoms and at least 40% by weight of branched fatty acidshaving eighteen carbon atoms, which mixture is liquid at roomtemperature.

The mixture of predominantly, preferably to the extent of at least 80%,branched fatty acids which contains at "ice least 95% by weight,preferably from 97 to 98% by Weight, of fatty acids having twelve toeighteen carbon atoms and which is liquid at room temperature shouldcontain at least 40% by weight, preferably from 50 to by weight, ofbranched fatty acids having eighteen carbon atoms. A very suitablemixture of predominantly branched fatty acids consists of about 1 to 3%by weight of C fatty acids, 6 to 15 by weight of C fatty acids, 12 to20% by weight of C fatty acids, 50 to 80% by weight of C fatty acidswhich are branched to the extent of at least preferably 99%, and about 1to 3% by weight of higher fatty acids. It is liquid at room temperature,for example at from 10 to 27 C. It is preferred to use methylated fattyacids such as isostearic acid as the branched C fatty acid, althoughmore markedly branched fatty acids are also suitable. The proportion oflinear fatty acids should preferably not exceed 20% by weight and inparticular should not exceed 15% by weight of the total mixture.

The said mixtures are advantageously used in the production of themagnetic layer in an amount of from 2 to 10% by Weight, preferably from3 to 8% by weight based on the dry weight of the magnetic layer. Amountsof 9 to 10 parts by weight of magnetic pigment, particularly iron oxide,about 3 parts by weight of binder and about 0.5 to 1.2 parts by weightof fatty acid mixture to be added according to the invention have provedto be very suitable.

It has proved to be advantageous in the production of the magnetic layerin the conventional equipment to disperse the magnetic pigment with thebinder together with an amount of an organic solvent sufficient forsetting up a favorable viscosity and with the fatty acid mixture usedaccording to this invention. After the components have been dispersed,the dispersion of the magnetic pigment can be applied by a conventionalcoating machine to a non-magnetizable base or another appropriatesupport. It is advantageous to orientate the magnetic particles afterthe dispersion has been applied to the backing by passing the appliedcoating through a magnetic field.

Suitable organic solvents for the produciton of the dispersions areorganic solvents known for this purpose, particularly aromatichydrocarbons, such as benzene, toluene or xylene; alcohols, such aspropanol or butanol; ketones such as acetone or methyl ethyl ketone;ethers, such as tetrahydrofuran; and mixtures thereof and other solventsor solvent mixtures commonly used for binders for surface coatings.

Particulate rod-shaped gamma-iron (III) oxide having an average particlesize of 0.1 to 2 mircons, particularly from 0.1 to 0.9 micron, ispreferred as magnetic pigment. Cube-shaped gamma-iron (Ill) oxide,particulate alloys of heavy metals known for this purpose, particularlyalloys of iron, cobalt and/or nickel, and ferromagnetic chromium dioxideare also suitable as magnetic pigments for magnetic recording mediaaccording to this invention.

Other fillers or pigments, such as carbon black, graphite, quartz powderand/or non-magnetizable powder based on silicates, as further additives,may be added in a conventional manner to the dispersions for theproduction of the magnetic layers, but the amount of these additivesshould advantageously not exceed 12% by weight and preferably should notexceed 8% by weight, based on the dry Weight of the magnetic layer.

The binders for the dispersion of the particulate magnetic pigment maybe any of the binders conventionally .used in the production of magneticlayers which are subamount of vinyl chloride units in the molecule, forexample polyvinyl chloride or vinyl chloride copolymers with comonomers,such as vinyl esters of monocarboxylic acids having two to nine carbonatoms, esters of aliphatic alcohols having one to nine carbon atoms andethylenically unsaturated carboxylic acids having three to five carbonatoms, such as acrylic acid, methacrylic acid or maleic acid, or thesecarboxylic acids themselves, and vinyl chloride copolymers containinghydroxyl groups which may be prepared by partial hydrolysis ofcopolymers of vinyl chloride and vinyl esters or direct copolymerizationof vinyl chloride with monomers containing hydroxyl groups, such asallyl alcohol or 4-hydroxybutyl acrylate or Z-hydroxyethyl acrylate orthe corresponding methaciylates. Vinyl chloride polymers of the saidtypes are particularly suitable as binders for the magnetic layer ofmagnetic recording media according to the invention.

In the production of flexible magnetic recording media using bindersbased on vinyl chloride polymers, generally about 2.5 to 4.5 parts byweight of binder is used for about to 13 parts by weight of gamma-iron(III) oxide as magnetic pigment. When the type of binder and/or magneticpigment is changed, their ratio to each other is adapted to the changein the specific density of the magnetic pigment and/or binder.

Conventional non-magnetizable backings or supports for the magneticlayer may be used, preferably flexible bases such as film or tape basedon polyvinyl chloride or polyesters, such as polyethylene terephthalatefilm of the usual thickness. Application of an adhesion-promotingintermediate layer, for example a layer based on a vinylidene chloridecopolymer, to the backing prior to application of the magnetic layer ispossible and some times advantageous.

After the magnetic layer has been applied, its surface mayadvantageously be finished in a conventional manner and the coated filmcan then be cut to the desired tape width in equipment conventionallyused for the production of magnetic recording media.

Magnetic recording media according to the invention are superior toprior art magnetic recording media of comparable type in that they havea longer life and exhibit great reliability in operation, even whenclimatic conditions fluctuate and atmospheric humidity is high. Magnetictapes according to the invention can be used at 95% relative humidityand 40 C. in an endurance test of more than five days without the tapeguides or heads (which comprise, inter alia, easily corroded zincinjection moldings) exhibiting corrosion phenomena or deposits in theform of abraded material from the magnetic layer. In a test at roomtemperature, a magnetic recording medium according to the invention inthe form of a 760 meter tape with a 10 kc./s. signal was played back ona four-track tape recorder at a speed of 9.5 cm./ second, the tape beingreversed automatically to rapid rewind or renewed playback for a periodof ten days. During the ten-day test, there were no short-term orlongterm decreases in the output level which exceeded 10% and after theten-day test all parts of the equipment, which had been in contact withthe tape such as heads, capstans or tape guides, were so clean that nocleaning was required.

Repetition of the test in a chamber in which a powerful ultraviolet lampprovided an atmosphere enriched with ozone did not give any indicationof a detrimental change in tapes according to this invention.

Magnetic recording media according to this invention in tape form aremoreover distinguished by improved recording of high frequencies.

The invention is illustrated by the following examples in which theparts and percentages are by weight unless otherwise stated. Parts byweight bear the same relation to partsby volume as the kilogram to theliter. The wear properties of the magnetic recording media in sustainedoperation were tested at room temperature and at 40 C.

and relative humidity on a wide variety of commercial tape recorders, asdescribed above.

EXAMPLE 1 900 parts of a particulate acicular gamma-ferric oxide havinga mean needle length of less than 0.8 micron is dispersed with 850 partsof tetrahydrofuran and 850 parts of toluene in which is dissolved 280parts of a copolymer having 91% of vinyl chloride units, 3% of vinylacetate units and 6% of vinyl alcohol units in a ball mill having acapacity of 6000' to 10,000 parts by volume and filled with 8000 to12,000 parts of steel balls, with an addition of a 75 parts of a liquidmixture of 2% of C fatty acids, 9% of C fatty acids, 15% of C fattyacids, 72% of C fatty acids consisting to the extent of 99% of branchedfatty acids and 2% of higher fatty acids which consists to the extent ofabout 92% of branched fatty acids, until a smooth, homogeneous surfaceis obtained when the dispersion is applied with a hand coater. After thedispersion has been filtered through a layer of cellulosic and asbestosfibers, it is applied to a polyethylene terephthalate film, passedthrough a magnetic field to orient the particles and dried at about C.The finished magnetic layer has a thickness of 10 microns. The film iscut into tapes 6.25 mm. in width which are tested as described above.Neither after five days at 40 C. and more than 95% relative humidity,nor after ten days at room temperature are there deposits or corrosionon the parts of the equipment coming into contact with the tape or anyother defects in the quality of reproduction of the recording. Exudationof the added fatty acid mixture was not observed. The tapes also exhibita particularly favorable recording sensitivity for short wavelengths.

Comparative tests 1 and 2 Example 1 is repeated but in Test 1 isopropylmyristate and in Test 2 stearyl stearate is used instead of the mixtureof branched fatty acids. Audio tapes made therewith are distinctlyinferior in sensitivity to those made according to Example 1 and exhibitdistortion. Moreover, they clog the heads and cause appreciable depositson those parts of the apparatus with which they come into contact.

EXAMPLE 2 Example 1 is repeated and 900 parts of the same iron oxide isdispersed for a number of days together with 300 parts of a copolymer of80% of vinyl chloride, 10% of diethyl maleate and 10% of dimethylmaleate and 2800 parts of a mixture of equal parts of tetrahydrofuranand toluene with an addition of 20 parts of very fine carbon black and100 parts of the fatty acid mixture of Example 1. The production of themagnetic recording medium with the resulting dispersion is carried outas described in Example 1. Magnetic recording media are obtained whichin the endurance tests have practically the same good properties as thetapes made according to Example 1.

Comparative tests 3 and 4 The procedure of Example 2 is repeated but inTest 3 n-stearic acid and in Test 4 a mixture of stearic acid withparaffin wax is used instead of the mixture of branched fatty acids.Audio tapes prepared therewith, as compared consisting essentially of amixture of predominantly branched fatty acids containing at least 95% byweight of fatty acids having twelve to eighteen carbon atoms and atleast 40% by weight of branched fatty acids having eighteen carbonatoms, which mixture is liquid at room temperature.

2. Magnetic recording media as in claim 1 wherein the mixture of fattyacids contains at least 80% by weight of branched fatty acids havingtwelve to eighteen carbon atoms.

3. Magnetic recording media as in claim 1 containing a mixture of about1 to 3% by weight of C fatty acids, 6 to 15% by weight of C fatty acids,12 to 20% by weight of C fatty acids, 50 to 80% by weight of C fattyacids which are branched to the extent of at least 95%, and about 1 to3% by weight of higher fatty acids.

4. Magnetic recording media as in claim 1 wherein said binder is a vinylchloride polymer having a predominant amount of vinyl chloride units inthe polymer chain.

5. Magnetic recording media as in claim 1, wherein the branched fattyacid having eighteen carbon atoms is isostearic acid.

6. Magnetic recording media as in claim 1, wherein the mixture ofpredominantly branched fatty acids contains to by weight of isostearicacid.

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